Rechargeable nickel-metal hydride (Ni-MH) batteries are used in a variety of industrial and commercial applications such as fork lifts, golf carts, uninterruptable power supplies, pure electric vehicles and hybrid electric vehicles. Vehicular applications include applications related to propulsion as well as applications related to starting, lighting and ignition (“SLI”). The Ovonic Battery Company (“OBC”) has developed high energy and high power nickel-metal hydride batteries for many different applications. Extensive research has been conducted by OBC scientists and engineers in improving all aspects of battery operation.
One aspect of battery operation that is particularly important for electric vehicle and hybrid vehicle applications is that of thermal management. In both electric and hybrid vehicle applications individual electrochemical cells are bundled together in close proximity. Many cells are both electrically and thermally coupled together. Therefore, the nickel-metal hydride batteries used in these applications may generate significant heat during operation. Sources of heat are primarily threefold. First, ambient heat due to the operation of the vehicle in hot climates. Second, resistive or I2R heating on charge and discharge, where I represents the current flowing into or out of the battery and R is the resistance of the battery. Third, a tremendous amount of heat is generated during overcharge due to gas recombination.
While issues regarding heat dissipation are generally common to all electrical battery systems, they are particularly important to nickel-metal hydride battery systems. This is because Ni-MH has a high specific energy and the charge and discharge currents are also high. Second, because Ni-MH has an exceptional energy density (i.e. the energy is stored very compactly) heat dissipation is more difficult than, for example, lead-acid batteries. This is because the surface-area to volume ratio is much smaller than lead-acid, which means that while the heat being generated is much greater for Ni-MH batteries than for lead acid, the heat dissipation surface is reduced.
In addition, while the heat generated during charging and discharging Ni-MH batteries is normally not a problem in small consumer batteries however, larger batteries (particularly when more than one is used in series or in parallel) generate sufficient heat on charging and discharging to affect the ultimate performance of the battery.
Thermal management issues for nickel-metal hydrid batteries are addressed in U.S. Pat. No. 6,255,015, in U.S. patent application Ser. No. 09/861,914 and in U.S. patent application Ser. No. 10/391,886. U.S. Pat. No. 6,255,015, U.S. patent application Ser. No. 09/861,914 and U.S. patent application Ser. No. 10/391,886 are all incorporated by reference herein.
Thus, there exists a need in the art for a battery design which reduces the overall weight thereof and incorporates the necessary thermal management needed for successful operation in electric and hybrid vehicles, without reducing its energy storage capacity or power output. One such battery design is a monoblock battery. An example of a monoblock battery is provided in U.S. Pat. No. 5,356,735 to Meadows et al, which is incorporated by reference herein. Another example is provided in U.S. Pat. No. 6,255,015 to Corrigan et al, which is hereby incorporated by reference herein. Another example is provided in U.S. Pat. No. 6,255,015 to Gow et al, which is hereby incorporated by reference herein. The present invention is directed to a additional improvements for battery cases.